1. Field of the Invention
The present invention relates to a bidirectional shape memory actuator having specific physical and mechanical properties and, more particularly, to the positioning of a moveable member, such as a vent control, using a shape memory actuator.
2. Description of the Prior Art
Shape memory elements have been used to open and close vent dampers as shown and described in U.S. Pat. No. 4,284,235 entitled "Vent Control Arrangement for Combustion Apparatus" issued on Aug. 18, 1981. In the arrangement disclosed in this patent, a helix made of a shape memory material is used to open a damper plate. The damper plate is normally in a closed position and opened by heating the helix to the deformation temperature so that it deforms to rotate the damper plate to a fully opened position. A lever mounted on the helix, on reaching the fully open position, closes a limit switch that activates a solenoid actuated gas valve to light the burner. The helix remains energized until the heat requirement is satisfied. The holding circuit is then opened. As the helix cools down, it will rotate the damper to the closed position.
In a device of the type shown in U.S. patent application Ser. No. 276,698 entitled "Personal Environmental Module" filed on Nov. 28, 1988, and assigned to the same assignee, dampers are used to control the air flow rate of cool air and room air into the module to meet the personal requirements of the individual working in the work station. In this type of device motor controllers were used to control the position of the damper plates and thus the temperature and air flow rate of the air passing through the dampers. Accurate control of the position of the damper plate is critical to the success of the module. The electric motors have a limited life, are noisy and expensive and also require periodic maintenance.